The present invention relates to an alloy comprising a miscible polymer blend of polyvinylidene fluoride ("PVDF") and aromatic polyimide compounds which has superior characteristics for mechanical strength, and provides greater hardness and heat resistance. The invention surprisingly reveals that miscible aromatic polyimide compounds are effective nucleating agents for PVDF crystallization and, thus, forming the miscible polymer blend by blending of the aromatic polyimide compound with PVDF affects nucleation of PVDF crystallization.
PVDF has application in the construction industry as an architectural coating because its excellent weatherability provides for long lasting coatings. PVDF and PVDF alloys can be formed into extrusion molded products. PVDF is widely used in the chemical processing industry for piping and valves and as the lining and coating material for storage tanks and reaction vessels because of its mechanical strength and resistance to chemical degradation. PVDF also possesses desirable electrical properties for use as jacketing materials in wire and cables.
PVDF has a glass transition temperature around -45.degree. C. and is a rubbery material in its amorphous state at room temperature. PVDF has high crystallinity in its solid state which results in a high modulus and good mechanical strength. PVDF is generally stable and resistant to weathering and thermal and chemical degradation. For certain applications, optical clarity of PVDF is a significant characteristic. Material strength, modulus, heat and thermal resistance and chemical resistance are significant criteria for the performance of PVDF as an architectural coating and in the chemical processing industry. The high heat resistance is a significant criteria for extrusion of PVDF materials as molded products.
Blending polymers has been an important industrial approach towards development of novel polymeric materials. PVDF has been identified as compatible with a few industrial polymers, including alkyl methacrylate and alkyl acrylates having carbon content on alkyl groups of less than 3. The polymers compatible with PVDF have the common characteristic of high concentrations of C.dbd.O groups, particularly on side chains of the carbon polymer. It is known from prior art that PVDF is compatible with poly(methyl methacrylate) ["PMMA"]. See, for example, U.S. Pat. No. 4,770,939. PVDF is compatible with acrylic resins because of hydrogen bonding between C.dbd.O groups of the acrylic resin and the CH.sub.2 groups of vinylidene fluoride. PVDF is also compatible with polyethyl methacrylate ("PEMA").
It is known in the art that PVDF can be miscibly blended with an acrylic resin at around a 70:30 ratio, by weight, of PVDF to acrylic resin to provide optimum coating performance with respect to criteria such as adhesion, toughness and optical clarity. Blending of PVDF with acrylic resins, however, generally results in reduction of modulus, heat resistance, hardness and abrasion or mar resistance compared to PVDF alone. The reduction of these properties serves to limit the application of PVDF blends.
It was recently disclosed in the art that PVDF can be blended with aromatic polyesters in the presence of a compatibilizing agent to develop PVDF alloys with good mechanical strength and impact resistance for use in the chemical processing industry and electrical industry as molded articles. (See, U.S. Pat. No. 5,496,889). It was recently found that PVDF blended with a compatible copolymer containing imide moieties results in a PVDF alloy of superior strength. (See, Lin, S. C. and Burkes, S. J., "Compatible Polyvinylidene Fluoride Blends with Polymers Containing Imide Moieties", application pending concurrently.) The present invention discloses that a miscible polymer blend of PVDF and an aromatic polyimide will create a PVDF alloy of superior mechanical strength, resulting in a material with greater heat and chemical resistance as compared with the prior art.
All percentages and ratios set forth herein are by weight/weight unless specifically designated otherwise.